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United States Patent | 5,042,948 |
Fletcher | August 27, 1991 |
A colorimeter provides compensation for changes in the color signature of an object due to lamp aging. A current measuring circuit measures current to the lamp during an initial training of the colorimeter and stores a value I.sub.T indicative of the lamp current at training. When an object is scanned by the colorimeter, lamp current is again sensed and assigned a value I.sub.S. Comparison between a sensed color signature and a stored color signature then occurs. Compensation is accomplished by modifying one of the two signatures by a ratio including I.sub.S and I.sub.T.
Inventors: | Fletcher; Thomas A. (Freeport, IL) |
Assignee: | Honeywell Inc. (Minneapolis, MN) |
Appl. No.: | 538363 |
Filed: | June 14, 1990 |
Current U.S. Class: | 356/328 |
Intern'l Class: | G01J 003/50 |
Field of Search: | 356/319,326,328,402,406,407,408,416,419,425 364/526,498 |
4076421 | Feb., 1978 | Kishner | 356/236. |
4449821 | May., 1984 | Lee | 356/319. |